How do you define consent though?
The capacity for linguistic understanding is a good starting point, following that the means to meta-perspective take over their own timeline.
Lets say I was traveling somewhere where English is not the native tongue, like Italy. If I can't speak Italian and a bunch of Italians are asking me if I want to fight their local champion in their native tongue, I can't really consent to it over not knowing what I'm agreeing to. If nothing around me is giving me hints as to what's going on, then I have no idea what I am agreeing or disagreeing with.
Consent requires a sense of awareness over what you're signing up for, and I don't think animals are at the level of signing contracts over themselves any more than children.You don't think they would be able to express "no I don't want to fight"?
It would be left ambiguous enough that they could have been groomed or trained into those responses, and with no capacity for language there's limited means of discerning that. With limited means of both comprehension and perspective taking it would be taking advantage of them even moreso than tricking a retarded person.
We aren't fine with human trafficking and other cruelties towards humans, why should it be okay towards animals?
Like, if you give them a coconut, they won't be able to understand what it means to consent to eating the coconut, so you can't give it to them? They'll take it from your hand.
They aren't consenting to anything big picture when they take the coconut, and if you told the animal that taking the coconut means that they belong to you now I don't think that's the deciding factor for them taking it or not.